An A record is probably the most common and easiest of all records to understand. Quite

simply, whatever is placed on the left will resolve to the IP address provided on the right.

Here’s an example of an A record:

www IN A 192.168.1.1

Here, www (expanded to include the full domain name) would resolve to 192.168.1.1.

If this were the zone file for example.org, www would be expanded to www.example.org. You could choose to be specific in your zone file and use something like this:

www.example.org. IN A 192.168.1.1

The final period (or dot) after .org is very important. If you left this out, the record

would be expanded to create www.example.org.example.org.

www IN A 192.168.1.1

CNAME

Cname collega due voci dns.

ftp IN CNAME www

The benefit with using CNAME is that if you change the IP address of the server (perhaps

you’re running this particular machine on an Internet connection that has a dynamic

IP address), you have to update only one IP address instead of two.

MX Records

mailserver.example.org. IN A 192.168.1.1

example.org. IN MX 10 mailserver

Remember, though, that the MX record must point to an existing hostname; in other words, it requires an A record. This doesn’t have to be in the same domain, as we’ll see in one of the following examples.

Se uno avesse due mail Server:

mailserver.example.org. IN A 192.168.1.1

mailserver2.example.org. IN A 192.168.1.2

example.org. IN MX 10 mailserver

example.org. IN MX 20 mailserver2

NS Records

An NS record looks like this:

example.org. IN NS dns0.example.com.

the authoritative name servers for our domain by creating to NS records.

Generally speaking, you should have at least two DNS servers. This is good practice

because if your DNS server goes down, people won’t be able to find your web site or your

e-mail servers. Because many people host their web sites in the same place they host their

DNS, this won’t help much, but it will ensure that e-mail is properly routed to the backup